Many electrical power sources have problems in matching production to demand. On a small scale, a solar power or wind turbine system that generates power on an intermittent basis, but nevertheless requires power on a broader demand basis. This problem is the same for the entire North American grid system where power producers are constantly trying to balance the power demand with many different integrated sources of power generation. A practical solution to this problem is needed. Several attempts at using various types of batteries (lead-acid, re-dox, etc.) have all been economic if not technical failures. The only current method of energy storage for load leveling is that known as pump-storage, in which energy is stored in the form of pumping water to a higher elevation and holding it in a reservoir. When the energy is required the water is allowed to fall to a lower reservoir while a water turbine extracts the energy. The round-turn efficiency of such a system is about 70%. In other words, for 100 kWh of electric energy put in, 70 kWh is generated. However, the principal problem with pump storage is that it requires large amounts of land that are not readily available at most generation sites.
Another approach to load-leveling which utilities have recently been using is “peaking turbines”. These are regular gas turbines connected to electrical generation equipment. The term “peaking” derives from the fact that these turbines can easily and quickly be turned on and off, and the power output regulated, and are used to provide power at times of “peak” demand. While peaking turbines do consume natural gas, which is becoming an expensive fuel, they can be installed for about $600/kW. The electrical switchgear adds another $400/kW. These are key economic marker for the utilities, and any load leveling system most be competitive with that $600-$1,000/kW value.
There is no presently known load leveling system that is competitive. Thus, in the U.S., the entire power production capability is actually double what is needed to meet the average demand, but still not enough to meet certain peaks since these peaks are often more than double the average need. Accordingly, capital equipment sits idle during non-peak periods, and is only used during peak periods, which is often less than a 10% duty-cycle.
Since the presently installed capacity is twice the needed average, the U.S. could meet all of its electrical needs for the next twenty years by installing load-leveling equipment, without the need to build any additional generating capacity. Such a system would be more robust, stable and energy efficient than the current power production grid system and can be accomplished without any infrastructure changes or dislocations. All that would be needed is to install load-levelers at various generation sites, and at points along the grid itself to create the required energy where it is needed, when it is needed, and simultaneously lower the stress on the weaker points of the grid. Some upgrade of the grid may be inevitable, but such a system would go a long way toward minimizing or postponing that inevitability.
While the present invention involves using liquid materials in a so-called re-dox configuration, there is a known conventional Vanadium based re-dox system which is described at www.vrbpower.com. This system uses conventional plate and frame configuration to move ionic liquids through a cell. The cell can either charge the liquids and store power, or it can withdraw power by discharging the liquids. However, these cells require a permi-selective membrane to separate the anolyte from the catholyte and this presents several problems. First, permi-selective membranes are very expensive, and result in the cost of any RedOx system being above $2,000/kW. Second, the membranes are prone to tearing from pressure differences. Third, the membranes do not scale-up well for the large sizes required in power plants, and using many small modules assembled into a large module results in a loss of the economy of scale. Fourth, liquid flow tends to be laminar thus promoting precipitation of material on the membranes, which produces clogs, and prevents proper functioning and raises the resistance of the cell. Thus, both initial costs and maintenance very high.
There are currently no large-scale electrolysis units suitable for integration with an electric utility. While there are some units which utilize membrane electrode assemblies (MEA's), these too are very expensive and unsuitable for scaling-up. Further, in an electrolysis cell there are three key sources of electrical losses, namely resistive, overpotential and polarization. Resistive losses occur when a current passes through any resistance. These losses are generally kept low by keeping resistance low. Overpotential is a phenomenon unique to electrochemical processes. In general when a gas is to be created out of a solution there tends to be an overpotential that is largely dictated by the material of the electrode surface. Platinized platinum has been found to be a material having the lowest overpotential for producing hydrogen from water. However, this material is clearly expensive, and its useful life is probably not sufficiently long enough under the conditions of a large-scale electrolysis. Polarization losses are caused by mass transport phenomena. Essentially ions need to be able to reach the electrodes in the cell. Anything that hinders this movement will create a situation where there are not enough ions present at the electrode to deliver the required current. There is a competition with consumed ions needing to move away from electrode sites while fresh one move in. If this is not met by natural convections, a field is formed that pulls in more ions. This field, however, requires energy and manifests itself as a lower voltage output, caused by polarization losses.
Most electrolysis technology currently employs a standard platinum-carbon coated Nafion MEA (membrane electrode assemblies) which can achieve about 1 watt per square centimeter at acceptable efficiencies of approximately fifty percent (50%). Accordingly, a megawatt system requires 1 million square centimeters or about 100 square meters of a product that costs over $30,000/square meter in large quantities. This amounts to a cost of over $3,000,000 per megawatt just for the membrane. The balance of the plant costs would easily double that amount to over $6,000,000 per megawatt. In a 1,000 megawatt plant the electrolysis unit would cost over $5 billion. Such costs are unacceptable. Further, MEA's have severe problems as they get larger, and therefore, capital costs on a per watt basis would not be expected to drop appreciably as the unit is scaled-up. Specifically, if the membranes are too large and the plates too close to achieve lower resistance, the flow rates required for gas and water become excessive and result in a premature failure of the membrane of which there are several modes including wear, tearing and freezing. Further, the maintenance and reliability of such MEA systems at the required scale are generally not acceptable. It is also well known that the MEA's are very susceptible to poisoning by almost all transition metal ions. This fact necessitates the use of a distilled water source to prevent the rapid degradation of the MEA. Systems that use platinized platinum in order to achieve lower potentials suffer from cost constraints, scalability problems and short life cycles of these fragile materials, all of which make these MEA systems unacceptable for large-scale systems.